1. Field of the Invention
The invention relates to switches and particularly to switches utilized for sensing a change in inertia. Certain aspects of the present invention are also applicable to switches utilized for purposes other than sensing a change in inertia.
2. Discussion of Background
Often it is desirable to sense a change in inertia for data gathering purposes and/or to initiate an automated sequence of events. For example, in one well-known application, an inertia switch can sense impact of a vehicle in order to actuate a safety device such as an air bag. In addition, in the context of rocketry and missiles, it can be desirable to determine the point at which a certain level of acceleration is attained in order to monitor the rocket or missile, as well as to initiate a sequence of controlled events which are to occur at a predetermined level of acceleration. An inertia switch may also be utilized in the shipping or automotive industries to indicate when predetermined acceleration levels are exceeded, for example in order to avoid excessive acceleration which may cause excessive loads on the engine. Inertia switches may also be utilized for armaments, such that detonation occurs upon impact, or a predetermined period after impact or after launch (e.g., in missile applications).
Typically, an inertia switch will include a mass which moves (i.e. moves relative to other portions of the switch) upon the application of a sufficient force/acceleration to the switch or the body to which the switch is attached. More particularly, when the switch attains a predetermined amount of acceleration, the mass within the switch will be moved to a position which either establishes or breaks an electrical contact in order to produce a signal.
U.S. Pat. No. 3,493,701 discloses an example of an inertia switch in which a magnet holds a ball in a seated position. When the switch encounters a predetermined amount of acceleration, the magnet will be insufficient to maintain the ball in the seated position, and the ball becomes unseated. Unseating of the ball will either break an electrical contact established in the seated position, or will establish a new electrical contact at a location other than the seated position. When functioning properly such an arrangement can provide an adequate indication of a change in inertia. However, it can be difficult to accurately maintain an exact magnetic force such that the ball is only unseated at a desired acceleration level.
In addition, the use of electrical circuit arrangements, in which contacts are established or broken upon acceleration, requires a voltage source which can increase the weight and complexity of the device. Additional monitoring or inspection is also required to ensure that the voltage source is functioning properly. Moreover, electrical contacts can often become oxidized or corroded, thereby diminishing the reliability of the switch. Such contacts are also susceptible to corrosion or dirt preventing proper contact.
Accordingly, a switch is desired which avoids the aforementioned shortcomings. Such a switch should be able to sense changes in inertia, or other conditions, without requiring a voltage source for producing a signal. In addition, the switch should be able to accurately sense changes in inertia without relying upon the establishment or breaking of electrical contacts within a circuit. The switch should also be reliable and inexpensive to build, and not susceptible to the production of an undesired signal as a result of vibration or other conditions which are not desired to be sensed.